This invention relates generally to fire dampers used in heating, ventilating and air conditioning systems at penetrations or openings through fire resistant walls, and particularly, to fire damper assemblies that are sealed in such wall penetrations.
Present fire prevention regulations require the presence of fire retardant walls throughout a building to prevent the spread of fire from one area of the building to another. These fire retardant walls include partitions between selected areas and floors and ceilings. Openings through these walls used for heating, ventilating and air conditioning are required to contain fire dampers, which normally provide free flow of air through the opening, but when activated by the heat of a fire, substantially close the opening. Ordinarily, sheet metal ducts containing the desired heating, ventilating and air conditioning air pass through these fire wall openings, but occasionally the duct is unnecessary and a clear passage opening through the wall is sufficient. When ducts are used, the fire damper is mounted interior of the duct at the opening through the wall. Otherwise, the fire damper is mounted directly in the wall opening.
Fire dampers, generally, are fabricated or formed of sheet metal to a box-like structure presenting a peripheral frame around a clear or open central passageway. Along one reach of the frame, interconnected sheet metal blades, louvers or baffles are held stored in place by a strap including a heat meltable link. A spring mechanism is connected to the blades so that when the link is melted by the heat of a fire, the spring mechanism positively moves the blades across the central passageway to close same. Another style of fire damper uses blades or louvers in a venetian blind arrangement to close the central passageway by rotation of the louvers upon melting of a link restraining a spring mechanism.
The blades and frame of the fire dampers are made of metal, usually a selected grade of steel, to withstand the high temperatures of a fire, while functioning to prevent the fire from passing through the barrier presented thereby. These high temperatures cause the parts of the fire damper to expand. Accordingly, installation of the fire damper in the wall opening requires an expansion space peripheral of the fire damper to insure proper operation of the blades when they are expanded by the heat. The expansion space is provided by cutting the wall opening larger than the fire damper height and width and using circumferential mounting flanges or collars to close off the expansion space otherwise providing another circumferential passage through the fire wall. In a duct mounting, the expansion space is exterior of the duct.
In certain critical buildings, such as nuclear power plants, the fire regulations recently have been changed to require sealing all wall penetrations with such as concrete, masonry or mineral fibers. Thus, the existing expansion spaces around fire dampers are being filled to seal the space around the fire damper, or the duct containing the interior mounted fire damper. Previously, this sealing had occurred in many locations, contrary to the manufacturers specifications. This possibly renders the fire dampers useless, thermal expansion of the parts without compensation can cause the blades to jam in the frame without completely closing off the central passageway. Such a possibility of fire damper non-operation is unacceptable in any environment, nuclear power plant or commercial office building. Thus, a fire damper is needed that can be sealed in the penetration through a fire wall without requiring an external expansion space.
Additionally, nuclear power plant regulations require that the building components, including fire dampers, survive or operate through severe seismic conditions, such as an earthquake. Thus, the fire damper mechanism must also be positively restrained to prevent its sheet metal parts from being battered to a non-operable condition by its unrestrained movement.
These requirements are equally applicable to commercial office space and nuclear power plant environments.